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Determination    and   Separations  of 
Gold  in  the  Electrolytic  Way. 


THESIS 

Presented  to  the  Faculty  of    the  Department    of    Philosophy  of  the 

University  of  Pennsylvania,  in  Partial  Fulfillment  of  the 

Requirements  for  the  Degree  of 

Doctor  of  Philosophy, 


BY 
SARAH  PLEIS  MILLER,  B.Sc. 

PHILADELPHIA,  PA. 

1904 


PHILADELPHIA 

THE  JOHN  C.  WINSTON  CO. 

1904 


Determination   and  Separations  of 
Gold  in  the  Electrolytic  Way. 


THESIS 

Presented  to  the  Faculty  of    the  Department    of    Philosophy  of  the 

University  of  Pennsylvania,  in  Partial  Fulfillment  of  the 

Requirements  for  the  Degree  of 

Doctor  of  Philosophy, 


BY 
SARAH  PLEIS  MILLER,  B.Sc. 

PHILADELPHIA,  PA. 

1904 


PHILADELPHIA 

THE  JOHN  C.  WINSTON  CO. 

1904 


a"? 


A 


This  investigation  was  undertaken  at  the  suggestion  of  Professor  Edgar 
F.  Smith,  and  has  been  pursued  under  his  direction.  I  wish  to  express  my 
appreciation  of  his  encouragement  and  unfailing  kindness. 


INTRODUCTION. 

It  has  long  been  known  that  gold  could  be  deposited  completely 
from  solutions  containing  it  in  the  form  of  double  cyanide,  sulphaurate, 
and  sulphocyanide,  as  well  as  in  the  presence  of  free  phosphoric  acid. 

Smith's  Electrochemical  Analysis,  3rd  Edition,  gives  an  example 
which  illustrates  the  conditions  with  which  a  good  result  may  be 
obtained  from  the  double  cyanide;  also  those  used  to  yield  satisfactory 
results  from  sodium  sulphide  solution. 

The  purpose  of  this  investigation  was  to  ascertain  the  conditions 
under  which  gold  could  be  satisfactorily  deposited  from  its  solution 
(a)  in  potassium  cyanide; 
(6)  in  the  presence  of  phosphoric  acid; 
(c)   in  sodium  sulphide; 

and  to  employ  the  data  thus  gathered  for  separations  of  the  metal 
from  various  other  metals. 


(3V 


173268 


GOLD  FROM  DOUBLE  CYANIDE  SOLUTION. 

DETERMINATION  OF  GOLD. 

The  determination  of  the  metal  from  its  double  cyanide  solution 
first  received  consideration: 

Smith's  Electrochemical  Analysis  gives  the  following  conditions: 
"The  solution  contained  0.1162  gram  of  metallic  gold;  to  it  were  added 
1.5  grams  of  potassium  cyanide  and  150  cc.  of  water.  It  was  heated 
to  55°  C.  and  electrolysed  with  a  current  of  N.D100  =  0.38  ampere 
and  2.7-3.8  volts.  The  precipitation  was  complete  in  one  and  one- 
half  hours;  and  the  deposit  weighed  0.1163  gram." 

To  10  cc.  of  auric  chloride  were  added  1.0  gram  of  potassium 
cyanide  and  150  cc.  of  water.  The  gold  precipitated  was  perfectly 
adherent  and  was  deposited  directly  upon  the  sides  of  the  platinum 
dish  in  connection  with  the  cathode. 


RESULTS. 


Gold 
present. 

Potassium 
cyanide. 

Dilution. 

Current. 

Volts.         T7Pera' 
ture. 

Time. 

Gold 
found  . 

Gram. 

Gram. 

cc. 

N.DIOO  = 

i    °- 

Gram. 

0.1275 
0.1275 

1.0 
1.0 

150 
150 

0.15-0.20  A 
0.20-0.30  A 

3.0-3.7              65 
3.5-4.0              65 

1  hour. 
1  hour. 

0.1275 

0.1277 

With  the  view  of  separations  that  might  possibly  be  made,  a  series 
of  experiments  were  next  carried  out,  employing  the  same  electrolyte 
as  prevailed  in  the  above  determinations,  but  using  a  current  of  low 
pressure  and  strength ;  in  order  to  'obtain  conditions  under  which  the 
lowest  possible  pressure  and  current  strength  would  be  applied  and  yet 
completely  precipitate  the  gold  from  its  solution. 

Many  trials  were  made  with  varying  conditions.     The  temperature 

(5) 


best  adapted  to  the  deposition  of  the  metal  ranged  between  55°  C.  and 
65°  C.  In  the  cold  the  gold  was  not  deposited  so  rapidly,  and  in  fact, 
for  the  lowest  amperage  and  voltage  employed  was  not  precipitated 
at  all.  A  temperature  above  75°  C.  also  prevented  to  some  extent  the 
deposition  of  the  gold. 

A  number  of  results  obtained  in  this  work  are  the  following : 


Number 
of  Exper- 

Gold 
present. 

Potas- 
sium 

Dilution. 

Current. 

Volts. 

Temper- 
ature. 

Time. 

Gold 
found. 

iment. 

cyanide. 

Gram. 

Gram. 

cc. 

N.DIOO  = 

°C. 

Hours. 

Gram. 

1  

0.1291 

1.0 

150 

0.07-0.09  A 

1.8-2.0 

75 

2* 

0.1288 

2  

0.1291 

1.0 

150 

0.04-0.06  A 

1.8-2.0 

68 

2* 

0.1293 

3  

0.1291 

1.0 

150      , 

0.02-0.15  A 

1.8-2.8 

60 

2 

0.1294 

4 

0  1291 

1  0 

150 

0.03-0.20  A 

2.0-3.0 

65 

2$ 

0  1290 

5 

0  1291 

1  0 

150 

0.11-0.04  A 

2.5 

61 

2 

0  1291 

6 

0  1291 

1.0 

150 

0.03-0.02  A 

1.8 

70 

2i 

0.1290 

7  

0.1291 

1.0 

150 

0.04-0.02  A 

1.8 

65 

2* 

0.1292 

In  experiments  1,  2  and  3,  tabulated  above,  a  current  of  N.D100 
=  0.015  A  and  voltage  of  1.6  was  allowed  to  act  upon  the  solution 
for  one  hour;  at  the  expiration  of  that  time  no  gold  had  been  precipi- 
tated. 

It  was  also  found  that  a  current  of  N.D100  =  0.02  A,  and  1.8 
volts,  although  sufficient  to  give  a  deposition  of  gold,  failed  to  bring 
down  the  last  traces.  This  was  demonstrated  by  subjecting  the  solu- 
tion to  those  conditions  for  three  hours,  and  then  raising  the  level  of 
the  liquid.  After  one  hour,  there  being  no  further  precipitation  of 
metal,  the  liquid  was  siphoned  off,  the  electrolyte  replaced  by  water, 
the  current  interrupted  and  the  deposit  weighed  after  washing  with 
hot  water,  alcohol  and  ether  and  drying  in  a  desiccator.  Instead  of 
0.1291  gram  of  gold  present  there  was  obtained  (a)  0.1260  gram  and 
(6)  0.1259  gram  of  metal. 

As  shown,  however,  in  experiments  6  and  7,  a  current  of  1.8  volts 
with  amperage  of  0.02-0.04  for  one  and  one-half  hours,  and  then 
increased  so  as  to  maintain  a  voltage  of  1.8,  allows  of  the  complete 
precipitation  of  the  gold. 


The  method  of  treating  the  depositions  of  metal  as  outlined  in 
the  above  was  adhered  to  in  all  experiments,  unless  otherwise  stated. 
And  in  all  case**  (unless  special  treatment  is  cited)  the  gold  was  depos- 
ited directly  upon  the  platinum;  and  the  gold  dissolved  off,  after  weigh- 
ing, by  introducing  very  dilute  potassium  cyanide  (0.5  gram  in  150  cc. 
of  water)  into  the  dish,  and  connecting  the  latter  with  the  anode  of  a 
battery  yielding  a  very  feeble  current  (0.2  A  and  5.0  volts),  using  a 
copper  wire  in  connection  with  the  cathode.  The  time  required  to 
thus  dissolve  the  gold  from  the  dish  was  (for  0.1291  gram)  one  hour. 

RATE  OF  PRECIPITATION  OF  GOLD  FROM  DOUBLE  CYANIDE 
SOLUTION. 

In  a  series  of  experiments  made  to  determine  the  rate  of  precipita- 
tion of  gold  from  its  double  cyanide  solution,  a  solution  containing 
0.1236  gram  of  gold,  1.0  gram  of  potassium  cyanide  and  diluted  to 
125  cc.  was  acted  upon  by  a  current  of  N.D100  =  0.03  A  and  2.5  volts. 
The  electrolyte  was  warmed  to  50°  C.  before  subjecting  it  to  the  current. 

After  15  minutes  there  was  no  deposit  of  gold. 

"     30  "  the  deposit  of  gold  weighed 0.0008  gram. 

"     45  "  the  deposit  of  gold  weighed 0.0030  " 

"     60  "  the  deposit  of  gold  weighed 0.0051  " 

"     75  "  the  deposit  of  gold  weighed.  ...  0.0083  " 

"     90  "  the  deposit  of  gold  weighed 0.0418  " 

"   105  "  the  deposit  of  gold  weighed 0.1047  " 

"135  "  the  deposit  of  gold  weighed...  .  0.1236  " 

"150  "  the  deposit  of  gold  weighed...  .  0.1236  " 


CURVE  SHOWING  THE  RATE  OF  PRECIPITATION  OF  GOLD  FROM  DOUBLE 

CYANIDE  SOLUTION. 

CURRENT      USED    —   hi  I>o(,  -    0.03    AMPERE    AND    2.5    VOL^S 


!  II  !  I  1  I  1  8     !       ?  =  =   = 


6  c  ci 


SEPARATIONS  IN  DOUBLE  CYANIDE. 

In  the  American  Chemical  Journal,  13,  417,  Smith  and  Muhr 
report  the  separation  of  gold  from  palladium,  platinum,  zinc,  cobalt, 
nickel  and  copper.  The  conditions  for  these  same  separations,  in 
terms  of  ampere  and  volt,  will  be  found  in  the  Journal  of  the  American 
Society,  21,  921,  922  and  923;  and  in  Smith's  Electrochemical  Analysis, 
pages  175  and  176. 

That  there  still  exist  gaps,  in  a  possible  list  of  metals  associated 
with  gold,  where  no  separations  are  recorded,  is  evident. 

Those  conditions  which  allow  of  the  separation  of  gold  from 
copper,  have  been  stated  to  serve  equally  well  for  the  separation  of 
gold  from  molybdenum,  tungsten  and  osmium. 

Among  the  metals,  not  as  yet  successfully  separated  from  gold, 
may  here  be  mentioned,  iron,  cadmium,  silver,  lead  and  mercury. 

GOLD  FROM  IRON. 

The  separation  of  silver-  from  iron  when  present  as  a  ferrous  salt, 
is  given  on  page  172  of  Smith's  Electrochemical  Analysis,  and  it  was 
thought,  that  under  similar  or  nearly  similar  conditions,  the  separation 
of  gold  from  iron  might  be  accomplished. 

Ferrous  ammonium  sulphate  was  taken  in  sufficient  quantity  to 
yield  0.1300  gram  of  metallic  iron,  and  dissolved  in  10  cc.  of  water, 
filtered  immediately  into  3.0  grams  of  potassium  cyanide,  warmed 
and  quickly  filtered — this  procedure  insured  the  presence  of  all  of  the 
iron  in  the  ferrous  state.  To  this  dark  brown  solution  were  added 
10  cc.  of  auric  chloride,  containing  0.1286  gram  of  metallic  gold,  and 
the  whole  diluted  to  125  cc. 

RESULTS. 


Number 
of 
Experi- 
ment. 

Gold 

present. 

Iron 
present. 

Potas- 
sium 
cyanide. 

Dilu- 
tion. 

Current. 

Volts. 

Tem- 
pera- 
ture. 

Time. 

Gold 
found. 

Gram. 

Gram. 

Gram. 

cc. 

N.D100  = 

°C. 

Hours. 

Gram. 

1  
2  
3  

0.1286 
0.1286 
0.1286 
0.1286 

0.1300 
0.1300 
0.1300 
0.1300 

3.0 
3.0 
3.0 
3.0 

125 
125 
125 
125 

0.1  3-0.36  A 
0.06-0.11  A 
0.17-0.30  A 
0.11-O.12  A 

2.3-3.0 
2.3-3.0 
2.5-3.0 
2  2-3.0 

65 
Cold 
64 
Cnld 

2* 

Night. 
3 
Niirht. 

0.1284 
0.1285 
0.1285 
0.1284 

10 

By  several  experiments  it  was  demonstrated  that  a  current 
of  N.D100  =  0.05-0.11  A,  and  1.7-2.3  volts,  other  conditions  as 
previously  given,  failed  to  completely  precipitate  the  gold;  0.1261 
gram  being  found,  0.1286  gram  being  present. 

In  all  four  experiments,  cited  above,  the  gold  was  completely  pre- 
cipitated from  the  solutions,  and  was  free  from  iron. 


GOLD  FROM  CADMIUM. 

There  is  no  separation  of  these  two  metals  in  alkaline  cyanide 
solution  recorded. 

The  following  suggestion,  which  was  thought  to  be  advantageous, 
in  the  separation  of  mercury  from  cadmium,  was  carried  out:  Before 
subjecting  the  electrolyte  to  the  action  of  the  current,  the  solution  was 
first  heated  to  60°  or  65°  C.  and  kept  at  that  temperature  throughout 
the  determination. 

Cadmium  sulphate  containing  0.1107  gram  of  cadmium,  and 
10  cc.  of  auric  chloride  (=  0.1200  gram  of  gold)  and  1.0  gram  of  potas- 
sium cyanide  with  a  total  dilution  of  125  cc.  constituted  the  electrolyte. 

Experiment  1. — A  current  of  N.D100  =  0.025  A  and  1.5  volts 
acted  upon  the  solution  for  one  hour;  at  the  expiration  of  that  time, 
there  being  no  deposit  of  gold,  the  current  was  increased  to  0.04  A  and 
1.6  V.  After  holding  the  current  at  the  latter  strength  for  one  hour, 
there  still  being  no  deposit  of  metal,  it  was  again  raised — giving  0.085  A 
and  1.8  volts,  when  cadmium  was  deposited  carrying  with  it  gold. 

Experiment  2. — A  small  platinum  spiral  anode  had  been  used  in 
the  preceding  experiment  (5  cm.  diameter).  In  this  second  trial  a 
platinum  wire  with  a  single  turn  was  connected  with  the  anode.  By 
this  means  a  lower  amperage  was  obtainable  for  a  corresponding  volt- 
age— however,  no  deposition  of  metal  occurred  until  the  current  regis- 
tered N.D100  =  0.035  A  and  1.8  volts — when  cadmium  and  gold  were 
simultaneously  precipitated. 


II 

Experiment  3. — The  solution  remaining  the  same  as  in  the  two 
preceding  experiments;  in  this  third  trial  a  straight  platinum  wire 
was  connected  with  the  anode  in  the  hope  of  obtaining  a  current  of 
sufficient  pressure  to  precipitate  the  gold,  but  of  current  strength  low 
enough  to  prevent  the  deposition  of  the  cadmium.  By  this  means  a 
current  of  N.D100  =  0.015  ampere  and  2.4  volts  was  obtained,  but 
at  the  expiration  of  one  hour  there  had  been  no  precipitation  of  metal. 
The  current  was  raised  to  0.028  ampere  and  2.5  volts;  after  one-half 
hour  to  0.03  ampere  and  2.8  volts.  A  deposition  of  gold  now  occurred. 
This  deposit  of  gold  did  not  seem  to  increase  in  quantity,  so  after  one 
hour  the  level  of  the  liquid  was  raised.  A  current  of  0.035  ampere  and 
3.0  volts  failed  to  give  a  further  deposit  of  gold.  On  increasing  it  to 
0.04  ampere  and  3.5  volts,  cadmium  was  precipitated  with  the  gold. 

Experiment  4.— Currents  of  N.D100  =  0.03  A  and  1.6  V  and 
0.04  A  and  1.8V  gave  no  precipitation  of  metal.  On  increasing  the 
current  to  0.05  A  and  2.0  V,  cadmium  and  gold  were  deposited  together. 

A  determination  was  next  made  with  the  same  electrolyte  that 
prevailed  in  the  four  preceding  experiments,  but  previous  to  the  pass- 
ing of  the  current  the  solution  was  not  warmed,  and  was  at  no  time 
above  50°  C.  In  this  case,  at  first  cadmium  alone  was  deposited ,  the 
current  equalling  0.02  A  and  1.5  volts.  After  one  hour  a  film  of  gold 
appeared  on  the  cadmium  deposit  and  increased  rapidly  in  amount  (the 
current  being,  at  the  time  of  the  appearance  of  the  gold,  0.03  A  and 
1.7  volts). 


CURVES  BASED  ON  THE  FACTS  OF  THE  PRECEDING  EXPERIMENTS. 

I. 

HBA.TGD       TO    70 a    C 

GOLD     AND     CADMIUM 


GOLD     AND     C  ADM  JVM 


OLD      AND    CADAOU.M 


CURVES  BASED  ON  THE  FACTS  OF  THE  PRECEDING  EXPERIMENTS- 

31 

IK    TKC    COLD 


0.04S 


0.035 


o.oas 


0.015 


GOID     AND     CADMIUM 


CADMIUM 


CGOLD    ANT)    CADMIUM 


VOLTS 


14 

Varying  the  amount  of  the  potassium  cyanide  was  tried.  One 
and  one-half  grams,  two  grams,  and  two  and  one-half  grams  were  used. 
In  all  of  these  trials  the  solutions  were  first  heated  to  60°  C.  A  current 
of  0.035  ampere  and  3.0  volts  caused  the  combined  precipitation  of 
cadmium  and  gold. 

Smith  and  Wallace,  Journal  of  Analytical  and  Applied  Chemistry 
(Jr.  An.  Ch.),  6,  87,  make  mention  that  in  the  separation  of  gold 
from  tungsten,  when  the  tungstic  acid  was  dissolved  in  caustic  alkali 
and  this  solution  then  added  to  that  of  the  gold,  the  gold  was  incom- 
pletely precipitated,  although  all  the  other  conditions  were  f avorabl  e 
to  its  complete  deposition. 

This  peculiar  behavior  of  the  gold  led  to  the  introduction  of 
definite  amounts  of  caustic  alkali  into  cadmium  solutions  of  known 
strength  and  containing  known  amounts  of  alkaline  cyanide.  For 
example,  a  current  of  0.015  to  0.02  A,  and  2.0  to  2.3  volts  acting  upon 
a  cadmium  sulphate  solution  (=  0.1107  gram  of  cadmium),  1.0  gram 
of  potassium  cyanide  and  2.0  grams  of  caustic  potash,  diluted  to 
125  cc.,  and  with  a  temperature  of  70°  C.  failed  to  give  any  precipita- 
tion of  cadmium. 

A  current  of  N.D100  =  0.025  A  and  2.5  V  with  other  conditions 
as  prevailed  in  the  preceding  experiment  gave  a  complete  deposition 
of  cadmium. 

It  was  hoped  from  the  above  observations  to  effect  a  separation 
of  cadmium  from  gold  by  the  retarding  action  of  the  potassium  hydrate 
upon  the  gold  or  more  probably  upon  the  cadmium. 

Experiment  5. — The  separation  of  gold  from  cadmium  was  now 
tried.  Cadmium  was  present  as  sulphate  (=  0.1107  gram  of  metal), 
gold  as  auric  chloride  (=  0.1286  gram  of  gold  in  10  cc.),  to  these  were 
added  1.0  gram  of  potassium  cyanide,  and  2.0  grams  of  caustic  potash. 
The  whole  diluted  to  125  cc.  and  heated  to  64°  C.  A  current  of  0.02 
ampere  and  1.6  volts  was  now  allowed  to  act  upon  the  solution,  the 
outer  circle  of  a  large  platinum  spiral  (of  four  turns)  being  in  connection 
with  the  anode,  this  spiral  was  changed  to  a  straight  wire  (3  cm.  of  its 


15 

length  being  immersed  into  the  solution)  which  then  gave  a  current  of 
N.D100  =  0.018  A  and  2.2  V.  Gradually  increasing  the  current  to 
6.02  A  and  2.4  V,  gave  no  deposition  of  metal.  With  0.02  A  and  2.5  V 

cadmium  and  gold  were  deposited  together. 

Experiment  6. — In  another  trial,  the  current  being  N.D100  = 
0.017  ampere  and  2.6  volts — other  conditions  as  above — cadmium  and 
gold  were  both  deposited. 

What  may  be  gathered  from  the  above? 

In  double  cyanide  solution,  as  may  be  observed  from  experiments 
1,  2,  3  and  4,  the  cadmium  with  N.D100  =  0.035  A  and  1.8-3.5 
is  invariably  deposited  with  the  gold,  which  fact  is  true  whether  the 
solution  be  heated  previously  to  the  passing  of  the  current,  or  whether 
this  condition  does  not  obtain.  It  is  also  true  for  the  presence  of  vary- 
ing amounts  of  potassium  cyanide  from  1.0  gram  to  2.5  grams.  But 
on  adding  2.0  grams  of  caustic  potash  in  presence  1.0  gram  of  potas- 
sium cyanide,  cadmium  is  not  precipitated  when  alone,  with  N.D100 
=  0.02  A  and  2.3  volts,  so  that  it  was  hoped  that  the  separation  could 
under  these  conditions  be  effected,  but  as  exhibited  in  experiments 
5  and  6,  when  the  metals  were  associated,  the  lower  current  conditions 
there  mentioned  are  useless — both  metals  being  precipitated,  there  being 
no  separation  of  cadmium  from  gold. 

GOLD  FROM  SILVER. 

In  connection  with  the  trials  for  the  separation  of  gold  from 
cadmium,  mention  has  been  made  of  the  work  of  Smith  and  Wallace, 
Jr.  An.  Ch.,  6,  87,  on  the  separation  of  gold  from  tungsten.  That 
work  also  led  its  authors  to  experiment  upon  gold  and  silver.  It  was 
found  by  their  researches,  Jr.  An.  Ch.,  6,  87,  that  a  "solution  contain- 
ing 0.1277  gram  of  gold,  in  the  presence  of  0.75  gram  of  potas- 
sium cyanide  and  acted  upon  by  a  current  of  1.8  cc.  electrolytic  gas 
per  minute,  precipitated  the  metal  fully  in  16  hours.  A  similar 
solution,  to  which  2.0  grams  of  caustic  potash  had  been  added,  when 
acted  upon  by  a  current  of  equal  and  even  greater  strength,  did  not 


i6 

yield  up  any  of  its  metal.  Silver  under  conditions  analogous  to  those 
described  for  gold,  was  fully  deposited  by  a  current  generating  1.4  cc. 
of  electrolytic  gas  per  minute.  .  .  .  To  10  cc.  silver  solu- 
tion (=  0.1090  gram  of  silver)  were  added  0.75  gram  of  potassium 
cyanide,  2.0  grams  of  potassium  hydroxide,  and  150  cc.  of  water.  The 
current  employed  gave  1.4  cc.  of  electrolytic  gas  per  minute.  The 
precipitated  silver  weighed  0.1085  gram.  Having  thus  found  such  a 
marked  difference  in  the  behavior  of  these  two  metals  under  the 
conditions  mentioned,  steps  were  taken  to  learn  what  the  results  would 
be  if  both  metals  were  present  together.  It  will  suffice  to  say  that 
their  separation  failed." 

It  was  found  by  the  authors  of  the  above  work,  that  in  many 
cases,  although  the  deposited  metal  was  perfectly  white  in  color,  after 
weighing  and  solution  in  nitric  acid,  to  be  simply  covering  a  layer  of 
gold. 

With  these  facts  as  a  basis,  solutions  of  gold  and  silver  were  sepa- 
rately subjected  to  the  current: 

A  silver  nitrate  solution  containing  0.1195  gram  of  silver  to  which 
had  been  added  1.0  gram  of  potassium  cyanide  and  2.0  grams  of  potas- 
sium hydrate  diluted  to  125  cc.  was  subjected  to  the  current. 

An  auric  chloride  solution  containing  0.1667  gram  of  gold  and 
1.0  gram  of  potassium  cyanide  and  2.0  grams  of  potassium  hydroxide, 
125  cc.  dilution,  was  similarly  treated. 

SILVER  ALONE  (0.1195  GRAM).  GOLD  ALONE  (0.1667  GRAM). 

Over  night  (cold) .  Over  night  (cold) . 

N.D100  =  0.009  to  0.015  ampere,  N.D100  =  0.01    ampere,    and 

and  1.6  to  1.8  volts.  1.6  volts. 

=  0.1190  GRAM  OF  SILVER  FOUND.  =  No  DEPOSIT. 

Heated  to  45°  to  50°  C.  Heated  to  45°  to  50°  C. 

N.D100  =  0.01  to  0.02  ampere,  N.D100  =  0.015  ampere,  and 

and  1.5  to  1.75  volts.  1.6  volts. 

=  0.1191  GRAM  OF  SILVER  FOUND.  =  No  DEPOSIT. 


17 

With  a  current  of  N.D100  =  0.025  to  0.03  ampere  and  2.0  to  2.5 
volts,  0.1579  gram  of  gold  was  deposited. 


As  will  be  observed  from  the  results  just  cited,  the  voltage  (1.8 
volts)  that  permits  of  the  last  traces  of  silver  being  deposited,  and  that 
which  would  allow  of  a  precipitation  of  gold  (2.0  volts),  are  very  close. 

With  these  facts  as  a  basis,  the  separation  of  silver  from  gold  was 
tried. 

The  problem  resolved  itself  into  the  effort  to  obtain,  as  far  as 
possible,  a  high  current  strength  with  a  very  low  pressure.  In  order 
to  obtain  such  a  relation  between  current  strength  and  pressure  the 
electrodes  were  varied  in  these  respects:  as  to  their  size  relation  and 
their  distance  apart;  the  electrolyte  was  changed  in  regard  to  propor- 
tions of  potassium  cyanide  and  caustic  potash  present. 

The  auric  chloride  used  contained  0.1200  gram  of  metallic  gold  in 
10  cc.;  2.0  grams  of  potassium  cyanide;  the  silver  nitrate,  containing 
0.1199  gram  of  silver;  2.0  grams  of  caustic  potash;  and  this  solution 
was  diluted  to  125  cc. 

Experiment  1. — At  5  o'clock  in  the  evening  the  above  solution 
was  subjected  to  the  action  of  the  current — N.D100  =  0.02  A  and 
1.5  volts.  A  perfectly  white  deposit  began  to  appear  almost  imme- 
diately. The  following  morning  the  current  registered  0.01  A  and 
1.4  V — and  there  was.  no  indication  of  any  metal  on  the  platinum  dish 
serving  as  cathode. 

Experiment  2. — The  same  electrolyte  as  used  for  experiment  1. 
A  temperature  of  45°  C.  was  maintained.  The  current  N.D100  = 
0.02  A  and  1.45  V  at  first  caused  precipitation  of  metal.  After  fifteen 
minutes  the  current  fell  to  0.015  A  and  1.3  volts,  and  the  deposit 
which  had  formed  was  redissolved.  The  current  was  raised  to  0.025  A 
and  1.5  volts^nd  deposition  of  metal  began.  After  two  hours  the  level 
of  the  liquid  was  raised.  There  seemed  to  be  no  further  deposition  of 


i8 

metal;  on  raising  the  current  to  0.03  ampere  and  1.8  volts,  however, 
more  metal  was  deposited.  In  one-half  hour  the  current  was  inter- 
rupted (after  first  siphoning  off  the  electrolyte  and  replacing  it  with 
water)  and  the  usual  procedure  of  treating  the  deposit  carried  out— 
when  the  deposit  appeared  a  uniformly  light  yellow  in  color.  It 
weighed  0.1973  gram,  the  liquid  was  free  from  silver,  hence  0.0774 
gram  approximately  of  gold  had  also  been  deposited. 

Experiment  3. — The  electrolyte  was  the  same  as  used  in  the  two 
preceding  experiments.  The  current  was  held  at  0.015  ampere  and 
1.6  volts  for  two  hours,  when  the  deposit,  after  washing  with  warm 
water,  alcohol  and  ether,  and  drying,  was  weighed.  There  had  been 
deposited  0.0935  gram  of  metallic  silver  (=  77%  of  silver  present) 
absolutely  free  from  gold. 

Experiment  4. — The  deposit  which  was  obtained  weighed  0.2003 
gram,  and  had  a  pale  yellow  color.  The  current  at  first  was 
N.D100  =  0.02  A  and  1.4V.  After  two  hours  this  was  increased 
to  0.025  A  and  1.7  V,  and  kept  there  for  one-half  hour.  There  was  no 
indication  of  silver  in  the  solution,  so  apparently  0.0804  gram  of  gold 
had  also  been  deposited. 

In  another  experiment  with  final  results  similar  to  those  of  experi- 
ments 2  and  4,  the  varying  effects  of  temperature  were  demonstrated. 
In  the  cold  a  deposition  of  silver  began  with  a  current  of  0.015  A  and 
1.45  V.  A  uniform  coating,  wrhite  in  appearance,  covered  the  dish. 
One  hour  later  this  had  entirely  disappeared.  Heat  was  applied  when 
the  deposit  again  appeared.  In  a  short  time  it  again  disappeared,  the 
temperature  registering  at  this  time  78°  C.  On  cooling  the  solution 
the  coating  again  appeared  and  remained  with  a  temperature  ranging 
from  45°  to  55°  C. 

With  all  of  the  preceding  trials  a  platinum  dish  of  175  cc.  capacity 
was  used  in  connection  with  the  cathode,  and  a  large  platinum  spiral 
of  7  cm.  diameter  in  connection  with  the  anode. 

Varying  amounts  of  potassium  cyanide  and  caustic  potash  were 
tried:  1.0  gram  of  potassium  cyanide  :  2.0  grams  of  caustic  potash; 


19 

3.0  grams  of  potassium  cyanide  :  2.0  grams  of  caustic  potash;  and  4.0 
grams  of  potassium  cyanide  :  2.0  grams  of  caustic  potash. 

In  all  the  same  results  could  be  recorded — failure  to  separate.  If 
a  low  enough  current  was  used  to  yield  silver  free  from  gold,  never 
more  than  80%  of  the  silver  was  deposited  from  its  solution.  When 
a  current  of  sufficient  strength  to  precipitate  the  last  traces  of  silver 
was  employed,  varying  amounts  of  gold  were  carried  down  with  the 
silver. 

Changes  in  the  electrodes,  and  with  each  of  these  changes  varia- 
tions in  the  proportion  of  potassium  cyanide  to  potassium  hydrate, 
were  next  tried,  as  follows: 

A  platinum  dish  of  175  cc.  capacity  was  made  the  anode,  a  plati- 
num gauze  (5  x  10  cm.)  the  cathode.  In  other  experiments  the  plati- 
num gauze  served  as  the  anode  and  the  dish  as  the  cathode. 

Two  plates  of  platinum  (5  x  10  cm.)  were  used,  the  one,  in  con- 
nection with  the  anode,  was  rolled  and  fastened  with  platinum  wire; 
the  other  surrounded  it,  being  equally  distant  from  it  at  all  points ;  a 
beaker  held  the  solution  into  which  the  electrodes  were  introduced. 

When  all  of  the  silver  was  precipitated  gold  was  invariably  present. 
In  some  cases,  the  deposit  was  perfectly  white  in  color,  but  when 
treated  with  nitric  acid,  the  silver  would  be  shown  to  have  been  cover- 
ing a  layer  of  gold.  Oftener,  however,  the  deposit  was  of  a  very  pale 
yellow  color,  when  in  response  to  treatment  with  nitric  acid  the  gold 
would  be  seen  as  a  thin  film  covering  the  silver.  In  a  few  cases  it 
seemed  probable  that  the  two  metals  had  been  simultaneously  pre- 
cipitated and  were  in  consequence  intimately  combined  in  the  deposit. 

The  expedient  of  first  coating  the  platinum  used  in  connection 
with  the  cathode  received  attention.  Varying  the  electrolyte  as  to 
relative  amounts  of  cyanide  and  caustic  potash  present;  and  also  vary- 
ing the  electrodes  as  has  been  described  above ;  in  t  his  case  also — 
but  with  no  better  results,  the  silver  and  gold  do  not  yield  to  separation. 

GOLD  FROM  MERCURY. 

In  the  Zeitsdirift  fur  physikalische  Chemie,  12,  113,  H.  Freuden- 
berg  reports  that  the  separation  of  mercury  from  gold  is  not  practicable. 


20 

In  the  paper  by  Smith  and  Wallace  in  the  Journal  of  Analytical 
and  Applied  Chemistry,  6,  87,  already  referred  to  under  the  discussion 
of  the  separation  of  gold  from  cadmium,  and  gold  from  silver,  the 
authors  report  having  tried  the  separation  of  gold  from  mercury  in 
cyanide  solution  containing  known  quantities  of  caustic  alkali.  The 
trials  were  fruitless  and  the  investigations  abandoned. 

As  the  result  of  several  experiments,  it  was  plainly  noticeable 
that  the  difference  between  the  amperage  and  voltage  where  the 
mercury  will  be  deposited  and  that  which  will  permit  of  the  precipita- 
tion of  gold  were  too  close  to  be  available  for  purposes  of  separations. 
Experiments  were  instituted  for  both  alkaline  cyanide  solutions,  and 
alkaline  cyanide  solutions  containing  known  quantities  of  potassium 
hydroxide ;  and  these  two  metals  are  yet  not  separated. 


IN  PHOSPHATE  SOLUTIONS. 

DETERMINATION  OF  GOLD. 

American  Chemical  Journal,  13,  206.  Smith  reports  "the  pre- 
cipitation of  gold  (0.1338  gram  of  gold)  from  a  solution  containing 
20  cc.  of  disodium  hydrogen  phosphate  (sp.  gr.  1.038)  and  3  cc.  of 
phosphoric  acid  (sp.  gr.  1.347).  Total  dilution  =  160  cc.  Current: 
0.8  cc.  OH  gas  per  minute.  The  deposit  weighed  0.1335  gram.  The 
filtrate  was  found  free  from  gold.  The  metallic  deposit  was  quite 
adherent  and  compact.  '  It  was  washed  with  hot  water." 

A  solution  containing  10  cc.  of  auric  chloride  (=  0.1286  gram 
metallic  gold),  20  cc.  of  disodium  hydrogen  phosphate  of  1.028  sp.  gr., 
and  5  cc.  of  phosphoric  acid  of  1.35  sp.  gr.,  was  diluted  to  125  cc., 
warmed  to  65°  C.  before  allowing  the  current  to  pass  through;  and 
electrolysed  with  a  current  of  N.D100  =  0.07  A  and  1.0  to  2.0  volts. 
After  one  and  one-half  hours  the  level  of  the  liquid  was  raised  and 
the  current  increased  to  N.D100  =  0.12  A  and  2.5  V.  There  was  no 
further  deposition  of  metal. 

The  deposit  was  brown,  and  in  washing,  with  the  alcohol  and  ether, 
some  of  it  was  detached.  The  current  used  had  evidently  been  too 
strong. 


21 


Other  experiments  followed,  using  a  lower  current;  in  these  the 
deposits,  although  more  compact  and  adherent,  warm  water  only  was 
used  for  washing,  were  not  of  bright  yellow  color.  Dark  specks 
appeared  on  the  deposits.  In  weighing  them,  they  were  all  found  to 
be  nearly  0.0008  gram  too  heavy. 

The  test  made  for  phosphoric  acid  in  the  deposited  gold  failed  to 
reveal  its  presence. 

A  solution  of  disodium  hydrogen  phosphate  and  free  phosphoric 
acid  was  electrolysed,  but  gave  no  deposit. 

Gently  igniting  the  dish  containing  the  deposit,  by  passing  it 
several  times  over  a  small  flame  of  a  Bunsen  burner,  gave  a  bright 
yellow  deposit  of  gold. 

A  deposit  weighing   0.0858  gram  was  thus  treated, 

and  weighed 0.0847  gram  after  the  first  heating, 

"       0.0846  gram  after  the  second  heating, 

"  "       0.0846  gram  after  the  third  heating. 

There  was  present  0.0849  gram  of  gold. 

The  gentle  ignition,  as  observed  from  the  three  weighings,  was 
not  sufficient  to  volatilise  any  of  the  gold,  shown  by  the  constant 
results  obtained.  The  excess  of  weight  of  deposit  being  probably  due 
to  traces  of  organic  matter  in  the  disodium  hydrogen  phosphate  or  in 
the  phosphoric  acid. 

RESULTS. 


Number 

• 

Diso- 

i 

Gold  found 

of 

Pnlrl 

dium 

Phos- 

Di- 

Tem- 

Experi- 
ment. 

present  . 

hydrogen 
phos- 

phoric 
Acid. 

lu- 
tion. 

Time. 

pera- 
ture. 

Current. 

Volts. 

Before 

After 

phate. 

Ignition. 

Gram. 

Sp.  Gr. 
1.028 

Sp.  Gr. 
1.35 

cc. 

Hours. 

CC. 

N.DIOO  = 

Gram. 

Gram 

1  

0.0849 

20  cc. 

5  cc. 

125 

2 

60 

0.02-0.015  A 

1.0-1.8 

0.0855 

00847 

2  

00849 

20  cc. 

5cc. 

125 

2 

67 

0.02  A 

1.0-2.0 

0.0857 

0.0848 

3  

0.1196 

20  cc. 

5  cc. 

125 

3 

60 

0.03  A 

1.0-2.0 

0.1204 

0.1197 

4  

0.1188 

20  cc. 

5  cc. 

125 

2 

64 

0.02-0.04  A 

1.6-2.0 

0.1196 

0.1187 

5  

0.1188 

20  cc. 

5  cc. 

125 

2 

60 

0.02-0.03  A 

1.0-2.0 

0.1192 

0.1185 

22 


In  all  of  these  the  deposits  were  perfectly  adherent  and  free  from 
phosphoric  acid,  and  after  heating  were  of  bright  yellow  color. 

SEPARATIONS  OF  GOLD  IN  PHOSPHATE  SOLUTION. 

Separations  have  been  effected  in  this  electrolyte,  as  will  be  found 
reported  in  the  American  Chemical  Journal,  13,  206,  by  Smith.  That 
of  gold  from  cadmium  was  found  to  be  unsuccessful.  The  gold  in 
separating  either  carrying  down  cadmium  or  separating  in  a  spongy 
mass,  this  last  occurrence  being  especially  noticeable  when  the  amounts 
of  phosphoric  acid  were  increased. 

GOLD  FROM  CADMIUM. 

Cadmium  sulphate  containing  0.1107  gram  of  cadmium  was  used. 
In  every  case  the  solution  was  previously  heated  to  50°-60°  C.  before 
allowing  the  current  to  act  upon  the  solution.  Disodium  hydrogen 
phosphate  (1.028  sp.  gr.)  and  phosphoric  acid  (1.35  sp.  gr.)  were  used 
in  amounts  of  40  cc.  of  the  former  and  10  cc.  of  the  free  acid;  30  cc. 
of  the  one  and  8  cc.  of  free  phosphoric  acid;  and  20  cc.  of  disodium 
phosphate  and  5  cc.  of  free  phosphoric  acid.  The  results  seemed  to 
be  equally  satisfactory;  20  cc.  of  disodium  hydrogen  phosphate  and 
5  cc.  of  phosphoric  acid  were  most  frequently  used. 

No  cadmium  or  phosphoric  acid  was  found  in  the  precipitated 
gold,  and  the  deposits  were  perfectly  compact  and  after  heating  bright 
in  appearance.  Warm  water  only  was  used  in  washing  all  deposits 
of  gold  from  phosphate  solution. 

RESULTS. 


Gold  found 

Gold 

Cadmium 

Dilution. 

Tempera- 

Time. 

Current. 

Volts. 

after 

present. 

present. 

ture. 

beatinj?. 

Gram. 

Gram. 

cc. 

°C. 

Hours. 

N.D100  = 

Gram. 

0.1188 

0.1107 

125 

60 

4 

0.02-0.03  A 

1.0-2.2 

0.1190 

0.1696 

0.1107 

125 

65 

4* 

002  A 

1.0-1.7 

0.1697 

0.1188 

0.1107 

125 

55 

5 

0.02  A 

1.1-2.0 

0.1187 

0.1448 

0.1107 

125 

66 

5 

0.03  A 

1.0-2.0 

0.1450 

0.1448 

0.1107 

125 

66 

4 

0.02  A 

1.0-1.8 

0.1447 

GOLD  FROM  IRON. 

Ferric  ammonium  sulphate  was  the  salt  used,  containing  0.1100 
gram  of  iron  in  10  cc.  Total  dilution  equalled  125  cc.  The  dish,  with 
the  deposited  gold,  was  gently  heated  as  described.  The  temperature 
was  52°  C.;  40  cc.  of  disodium  hydrogen  phosphate  (1.028  sp.  gr.)  and 
10  cc.  of  free  phosphoric  acid  (1.35  sp.  gr.)  and  0.1188  gram  of  gold 
were  present. 

The  current  acting  upon  the  solution  with  a  strength  of  N.D100 
=  0.03  to  0.06  ampere  and  1.2  to  2.0  volts  failed  to  precipitate  the 
last  traces  of  gold: 


Gold  found 
Gold  present 
Gold  found 
Gold  present 
Gold  found 
Gold  present 


0.1163  gram. 
0.1188  gram. 
0.1168  gram. 
0.1188  gram. 
0.1155  gram. 
0.1188  gram. 


The  solution  was  made  more  dilute,  and  the  current  increased 
especially  for  the  last  half-hour.  The  results  being  then  more  satis- 
factory. 

RESULTS. 


Number 
of 
Experi- 
ment. 

Gold 
present. 

Iron 
present. 

Dilution 

Time. 

Tem- 
pera- 
ture. 

Current. 

Volts. 

Gold  found 
after 
Ignition. 

Gram. 

Gram. 

cc. 

Hours. 

°C. 

N.D100  = 

Gram. 

1  

0.1188 

0.1100 

150 

6 

63 

0.02^0.  16  A 

1.0-3.6 

0.1182 

2  

0.1188 

0.1100 

150 

6 

67 

0.02-0.17  A 

1.0-3.0 

0.1190 

3  

0.1188 

0.1100 

150 

5 

62 

0.02-0.08  A 

1.0-2.7 

0.1189 

4  

0.1188 

0.1100 

150 

•    5 

62 

0.02-0.08  A 

1.0-2.7 

0.1189 

5  

0.1188 

0.1100 

150 

5 

62 

0.02-0.08  A 

1.0-2.5 

0.1187 

6  

0.1188 

0.1100 

150 

5 

63 

0.02-0.10  A 

1.0-2.7 

0.1185 

In  1  and  2  the  gold  was  not  perfectly  adherent.  The  current 
strength  was  lowered  and  in  3,  4  and  5  the  deposit  was  perfectly 
adherent,  of  a  bright  yellow  color  after  heating,  and  was  free  from  iron 
and  phosphoric  acid. 


GOLD  FROM  ZINC. 

In  the  American  Chemical  Journal,  13,  206,  Smith  states  that 
the  separation  of  gold  and  zinc  proceeded  without  the  least  difficulty. 
"  A  solution  of  150  cc.  volume  contained,  0.1336  gram  of  gold,  0.1500 
gram  of  zinc,  30  cc.  of  disodium  phosphate  (1.0358  sp.  gr.),  and  3  cc. 
phosphoric  acid.  It  was  electrolysed  with  a  current  giving  0.6  cc.  of 
OH  gas  per  minute.  The  gold  deposit  was  compact  and  readily 
washed  with  hot  water.  It  was  dried  over  a  warm  iron  plate.  It 
weighed  0.1338  gram,  zinc  was  not  precipitated." 

Zinc  sulphate  (=  0.1150  gram  of  zinc)  and  10  cc.  of  auric  chloride, 
30  cc.  of  disodium  hydrogen  phosphate  (1.028  sp.  gr.),  6  cc.  of  phos- 
phoric acid  (1.35  sp.  gr.)  were  diluted  to  150  cc. 

RESULTS. 


Gold 

Zinc 

Temper- 

Gold found 

present. 

present 

Time. 

ature. 

Curreut 

Volts. 

after 
heating. 

Gram 

Gram. 

Hours. 

°C. 

N.Dra,  = 

Gram. 

0.1148 

0.1150 

3* 

66 

0.03  A 

1.8-2.0                0.1151 

0.1148 

0.1150 

3 

61 

0.03-0.04  A 

1.0-20 

0.1145 

0.1117 

0.1150 

2 

69 

0.03-0.05  A            2.0-2.5 

0.1113 

0.1117 

0.1150 

2 

69 

0.03-0.05  A     !       2.0-2.5               0.1114 

0.1117 

0.1150 

2 

67 

0.04  A                2.0-2.5 

0.1115 

Zinc  was  not  found  to  be  present  in  the  precipitated  metal. 

GOLD  FROM  COBALT. 

Reported  in  the  same  paper  as  the  gold-zinc  separation,  American 
Chemical  Journal,  13,  206,  and  employing  the  same  conditions  as 
obtained  in  that  separation,  is  the  separation  of  gold  from  cobalt. 

It  was  found  after  repeated  experiments  that  the  separation  was 
effected  more  satisfactorily  in  rather  dilute  solutions.  Accordingly  a 
solution  of  auric  chloride,  30  cc.  of  disodium  hydrogen  phosphate  of 
sp.  gr.  1.028,  6  cc.  of  phosphoric  acid,  sp.  gr.  1.35,  and  cobalt  nitrate 
containing  0.1200  gram  of  cobalt  was  diluted  to  150  cc.  to  200  cc. 


25 

RESULTS. 


Gold 
present. 

Cobalt 
present. 

Time. 

Tempera- 
ture. 

Current. 

Volts. 

Gold  found 
after 
heating. 

Gram. 

Gram. 

Hours. 

°C. 

N.D100  = 

Gram. 

0.1219 

0.1200 

2* 

53 

0.03-0.04  A 

1.2-2.0 

0.1216 

0.1219 

0.1200 

4 

55 

0.04  A 

1.2-2.3 

0.1214 

0.1219 

0.1200 

3 

60 

0.03-0.04  A 

1.1-2.0 

0.1217 

0.1237 

0.1200 

2* 

78 

0.03  A 

0.8-1.8 

0.1235 

0.1237 

0.1200 

3 

58 

0.04-0.08  A 

1.1-2.2 

0.1238 

0.1237 

0.1200 

2 

66 

0.04  A 

1.1-2.0 

0.1236 

0.1237 

0.1200 

2 

62 

0.03-0.06  A 

1.1-2.0 

0.1239 

0.1237 

0.1200 

2 

58 

0.03-0.  Of,  A 

1.1-2.0 

0.1235 

Cobalt  was  not  precipitated. 


GOLD  FROM  NICKEL. 

Since  the  separation  of  gold  from  cobalt  had  been  effected  it  was 
natural  to  expect  a  like  result  for  gold  from  nickel. 

A  solution  of  150  cc.  volume  containing  0.1200  gram  of  nickel  as 
nickelous  nitrate,  40  cc.  of  disodium  hydrogen  phosphate  of  sp.  gr. 
1.028,  6  cc.  of  phosphoric  acid,  1.35  sp.  gr.,  10  cc.  of  auric  chloride 
containing  0.1236  gram  of  gold  was  electrolysed  with  the  following 
results : 


nnlH  found 

Gold 
present. 

Nickel 
present. 

Tempera- 
ture. 

Time. 

Dilution 

Current. 

Volts. 

after 
heating. 

Gram. 

Gram. 

°C. 

Hours. 

cc. 

N.DIOO  = 

Gram. 

0.1236 

0.1200 

55 

4 

150 

0.04-0.07  A 

0.8-2.4 

0.1232 

0.1236 

0.1200 

68 

4 

150 

0.04-0.06  A 

1.0-2.2 

0.1236 

0.1236 

0.1200 

62 

3 

175 

0.03-0.06  A 

1.0-2.0 

0.1239 

0.1236 

0.1200 

60 

2 

175 

0.03-0.06  A 

1.0-2.0 

0.1233 

The  gold  deposited  showed  no  trace  of  nickel. 


26 

GOLD  FROM  COPPER. 

The  electrolyte  consisted  of  copper  sulphate  (=  0.1200  gram  of 
copper),  40  cc.  of  disodium  hydrogen  phosphate,  1.028  sp.  gr.,  10  cc. 
of  phosphoric  acid,  1.35  sp.  gr.,  and  10  cc.  of  auric  chloride  (=  0.1188 
gram  of  gold).  Dilution,  125  cc. 

A  current  of  N.D100  =  0.03  A  and  2.0  V  acted  on  the  above 
solution  in  the  cold  through  the  night.  The  deposit  weighed  0.2047 
gram;  0.1188  gram  of  gold  being  present.  Copper  was«present  with 
the  gold. 

In  a  second  trial,  using  the  same  electrolyte  as  above,  but  a 
current  of  N.D100  =  0.02  ampere  and  1.0  volt,  with  a  temperature 
of  54°  C.,  after  three  hours  the  deposit  weighed  0.1112  gram  of  gold 
free  from  copper,  0.1188  gram  of  gold  was  present.  This  same  current, 
however,  failed  to  bring  down  the  last  traces  of  the  gold  from  its  solu- 
tion. 

In  all  precipitations  of  gold  from  acid  phosphate  solution,  a 
platinum  dish  of  175  cc.  to  200  cc.  capacity  was  used  in  connection 
with  the  cathode,  a  platinum  spiral  with  the  anode.  The  depositions 
were  washed  only  with  cold  and  warm  distilled  water  after  siphoning 
off  the  liquid  and  replacing  it  with  water.  They  were  also  heated 
gently  either  by  passing  the  dish  several  times  over  a  small  flame  of  a 
Bunsen  burner  or  by  placing  the  dish  on  a  warm  iron  plate. 


IN  SODIUM  SULPHIDE  SOLUTION 

In  Smith's  Electrochemical  Analysis  it  is  stated  "that  the  depo- 
sition of  gold  from  sodium  sulphide  solution  (sp.  gr.  1.18)  is  just  as 
satisfactory  as  that  of  gold  from  double  cyanide." 

The  conditions  given  for  the  current  are  0.1-0.2  ampere  for  a 
total  dilution  of  about  125  cc.  The  precipitated  metal  was  very 
adherent  and  of  a  bright  yellow  color. 


27 
DETERMINATION  OF  GOLD. 

A  solution  of  150  cc.,  in  which  were  0.1276  gram  of  gold,  15  cc.  of 
sodium  sulphide  (1.19  sp.  gr.),  heated  to  61°  C.  was  electrolysed  with 
a  current  of  0.1  A  and  0.1  -  0.2  A,  and  2.4  to  3.0  volts.  In  two  hours 
there  was  deposited  (1)  0.1272  gram,  and  (2)  0.1277  gram  of  gold. 

To  the  auric  chloride  were  added  50  cc.  of  water,  then  the  sodium 
sulphide  and  the  solution  warmed  carefully  until  it  became  clear,  and 
finally  diluted  to  150  cc.  and  electrolysed.  The  deposited  gold  is 
perfectly  adherent,  and  of  a  shining  yellow  color,  appearing  like 
polished  metal. 

The  sodium  sulphide  was  prepared  as  follows:  Sodium  hydrate, 
precipitated  from  alcohol,  in  a  solution  of  1.25  sp.  gr.  Saturate  one- 
half  the  quantity  of  the  solution  with  hydrogen  sulphide  and  filter 
quickly  into  the  remaining  one-half.  Pass  hydrogen  sulphide  through 
the  entire  solution  to  saturation,  filter  quickly.  The  yellow  liquid  is 
evaporated  over  a  free  flame  quickly  until  a  thin  film  forms  on  the 
surface.  Allow  the  liquid  to  crystallize,  redissolve,  heat  and  repeat 
the  crystallization  and  resolution  of  the  crystals  several  times,  then 
pour  the  hot  solution  (sp.  gr.  =  1.19)  into  glass-stoppered  bottles, 
which  are  sealed. 


SEPARATIONS  IN  SODIUM  SULPHIDE  SOLUTION. 

The  separation  of  gold  from  arsenic,  molybdenum  and  tungsten, 
may  be  effected  by  observing  those  conditions  given  for  the  determina- 
tion of  gold  from  its  sodium  sulphide  solution. 

Separations  of  gold  from  mercury  and  tin  have  not  been  effected. 


GOLD  FROM  MERCURY. 

The  solution  electrolysed  contained  10  cc.  of  mercuric  chloride 
(=  0.1300  gram  of  mercury),  25  cc.  of  sodium  sulphide  (1.19  sp.  gr.), 
10  cc.  of  auric  chloride  (  =  0.1276  gram  of  gold).  Total  dilution 
equalling  150  cc. 


28 

Several  trials  were  made  employing  a  current  of  N.D100  =  0.015 
to  0.03  ampere  and  1.1  to  1.7  volts.  In  every  case  gold  and  mercury 
were  precipitated  together. 

GOLD  FROM  TIN. 

The  many  trials  made  to  separate  these  two  metals,  in  sodium 
sulphide  solution,  resulted  in  failures.  Tin  being  deposited  with  the 
gold. 


™ E    '      \ 
UNIVERSITY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
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WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
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DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


APR  14    1933 
MAY    9    1948 

290*57*' 


REC'D 

OCT161957 


REC'D  LL> 

FBI  8 '64-12 1* 


LD  21-50m-l,'3 


